Method and apparatus for treating a hydrocarbon stream

ABSTRACT

A method of treating a hydrocarbon stream such as natural gas from a feed stream ( 10 ) comprising at least the steps of: a) passing the feed stream ( 10 ) through a distillation column ( 12 ) to provide a gaseous stream ( 20 ) and a C 2+  liquid stream ( 30 ); b) compressing at least part of the gaseous stream ( 20 ) through one or more feed compressors ( 14, 16 ) to provide a compressed stream ( 40 ); and c) commonly driving ( 28 ) at least one of the feed compressors with one or more separate refrigerant compressors for one or more separate refrigerant circuits, by mechanically interconnecting said compressors.

The present invention relates to a method and apparatus for treating ahydrocarbon stream such as natural gas, in particular in a process forthe production of liquefied natural gas.

Several methods of liquefying a natural gas stream thereby obtainingliquefied natural gas (LNG) are known. It is desirable to liquefy anatural gas stream for a number of reasons. As an example, natural gascan be stored and transported over long distances more readily as aliquid than in gaseous form because it occupies a smaller volume anddoes not need to be stored at high pressures.

U.S. Pat. No. 6,401,486 B1 relates to a method and apparatus for highrecovery of hydrocarbon liquids from methane-rich natural gases inassociation with liquefied natural gas production. FIG. 1 of U.S. Pat.No. 6,401,486 shows a pre-treatment process in a liquefaction plant inwhich the lighter stream from the NGL recovery column can bere-compressed by an expander/compressor. A problem of the arrangement inFIG. 1 is that the expander/compressor requires a separate driver priorto the refrigeration system. A driver is an expensive item both in termsof capital and running costs.

It is an object of the present invention to reduce the capital and/orrunning costs of a liquefaction plant involving liquefying apparatus.

It is a further object to provide an alternative method and apparatusfor liquefying natural gas.

One or more of the above or other objects can be achieved by the presentinvention providing a method of treating a hydrocarbon stream such asnatural gas from a feed stream comprising at least the steps of:

-   (a) passing the feed stream through a distillation column to provide    a gaseous stream and a C₂ ⁺ liquid stream;-   (b) compressing at least part of the gaseous stream through one or    more feed compressors to provide a compressed stream; and-   (c) commonly driving at least one of the feed compressors with one    or more separate refrigerant compressors for one or more separate    refrigerant circuits, by mechanically interconnecting said    compressors.

Refrigerant circuit(s) use large compressors which can be driven bypowerful drivers. Gas turbines are usually used to drive the compressorsas the gas turbines can be fuelled by feed gas, and in particularmethane extracted from feed gas.

It is also common to perform a number of pre-treatment processes on afeed stream such as natural gas liquid extraction prior to liquefaction,including separation or extraction of heavier hydrocarbon fractions.Many of such pre-treatment processes also require the use of compressorsdriven by drivers such as gas turbines.

As each and every gas turbine or other driver in a liquefaction plant isexpensive, this contributes a considerable percentage to the overallcapital and running costs of the cooling.

It has been surprisingly found that by combining the driver of at leastone of the feed compressors and at least one of refrigerant compressors,the capital costs can be reduced. Furthermore it has been found that theresultant ratio of compressor power input for the compressors can bebrought closer to an optimum ratio, hence reducing capital and runningcosts.

Refrigerant circuits are known in the art. They generally involve one ormore heat exchangers, one or more expansion devices or units, and one ormore compressors. Whilst each refrigerant circuit can be separate fromother refrigerant circuits, one or more parts of a refrigerant circuitcan be connected or interconnected with another refrigerant circuit(s),or at least involve an interconnection of actions or combination ofmaterials and/or flow with other circuit(s).

Each refrigerant circuit is separate from the pathway of the hydrocarbonstream and its treated and/or subsequent cooled and/or liquefied forms.Thus the or each refrigerant is not mixed with or directly derived fromthe hydrocarbon stream and its subsequent forms. That is, the fluidpassing through the or each relevant feed compressor is different to thefluid passing through the or each commonly driven refrigerantcompressor.

Preferably, the method further comprises the step of: cooling thecompressed stream by passing the compressed stream against one or morerefrigerants being in one or more of the refrigerant circuits.

In one embodiment of the present invention, the method of treating ahydrocarbon stream such as natural gas from a feed stream comprises atleast the steps of:

-   (a) passing the feed stream through a distillation column to provide    a gaseous stream and a C₂ ⁺ liquid stream;-   (b) compressing at least part of the gaseous stream through one or    more feed compressors to provide a compressed stream; and-   (c) cooling the compressed stream by passing the compressed stream    against one or more refrigerants being in one or more refrigerant    circuits involving one or more refrigerant compressors;    wherein at least one of the feed compressors in step (b) and at    least one of the refrigerant compressors in step (c) are    mechanically interconnected and are arranged to be driven by a    common driver.

Although the method according to the present invention is applicable tovarious hydrocarbon feed streams, it is particularly suitable fornatural gas streams to be cooled, and in particular liquefied. As theperson skilled in the art readily understands how to cool and liquefy ahydrocarbon stream, this is not further discussed here in detail.

Preferably, the cooling of the compressed stream involves at least twocooling stages, each stage including at least one refrigerant circuit.

More preferably, the cooling of the compressed stream involves onepre-cooling stage and one main cooling stage, and the or a feedcompressor of step (b) is mechanically interconnected with a refrigerantcompressor of the pre-cooling refrigerant circuit.

Pre-cooling of the feed stream can be carried out to reduce itstemperature to below 0° C., such as between −10° C. to −50° C.Preferably, the feed stream is cooled upstream of step (a) against atleast part of the gaseous stream produced in step (a).

Main cooling of a pre-cooled stream can be to further reduce itstemperature to below −100° C., such as between −120° C. to −170° C.

The person skilled in the art will readily understand that afterliquefaction, the liquefied natural gas may be further processed, ifdesired. As an example, the obtained LNG may be depressurized by meansof a Joule-Thomson valve or by means of a cryogenic turbo-expander.Also, further intermediate processing steps between the gas/liquidseparation in the distillation column and the cooling may be performed.

The hydrocarbon stream may be any suitable feed stream to be treated,but is usually a natural gas stream obtained from natural gas orpetroleum reservoirs. As an alternative the natural gas stream may alsobe obtained from another source, also including a synthetic source suchas a Fischer-Tropsch process.

Usually the natural gas stream is comprised substantially of methane.Preferably the feed stream comprises at least 60 mol % methane, morepreferably at least 80 mol % methane.

Depending on the source, the natural gas may contain varying amounts ofhydrocarbons heavier than methane such as ethane, propane, butanes andpentanes as well as some aromatic hydrocarbons. The natural gas streammay also contain non-hydrocarbons such as H₂O, N₂, CO₂, H₂S and othersulphur compounds, and the like.

If desired, the feed stream containing the natural gas may bepre-treated before passing it to the distillation unit. Thispre-treatment may comprise removal of undesired components such as CO₂and H₂S, or other steps such as upstream cooling, pre-pressurizing orthe like. These steps are well known to the person skilled in the art,they are not further discussed here.

Where upstream cooling is included, another embodiment of the presentinvention is a method of treating a hydrocarbon stream such as naturalgas from a feed stream further the step of:

cooling the feed stream upstream of step (a) by passing the feed streamagainst one or more refrigerants being in one or more of the refrigerantcircuits.

In this way, the present invention also provides a method of treatingcomprising at least the steps of:

-   (a) cooling the feed stream against one or more refrigerants being    in one or more refrigerant circuits involving one or more    refrigerant compressors;-   (b) passing the cooled feed stream through a distillation column to    provide a gaseous stream and a C₂ ⁺ liquid stream;-   (c) compressing at least part of the gaseous stream through one or    more feed compressors to provide a compressed stream; and-   (d) cooling the compressed stream;    wherein at least one of the feed compressors in step (c) and at    least one of the refrigerant compressors in step (a) are    mechanically interconnected and are arranged to be driven by a    common driver.

The term “natural gas” as used herein relates to anyhydrocarbon-containing composition which is at least substantiallymethane. This includes a composition prior to any treatment, suchtreatment including cleaning or scrubbing, as well as any compositionhaving been partly, substantially or wholly treated for the reductionand/or removal of one or more compounds or substances, including but notlimited to sulfur, carbon dioxide, water, and C₂ ⁺ hydrocarbons.

The compressors are mechanically interconnected in the sense that thereis physical linkage therebetween which relates motion therebetween.Preferably said mechanically interconnected compressors are arranged ona common drive shaft of the driver, further reducing the capitalinfrastructure.

The distillation column may be any column or arrangement adapted toseparate the feed gas into a gaseous stream, which will generally bemethane-enriched, and a C₂ ⁺ liquid stream, which will generallyhave >40 mol % of one or more hydrocarbons heavier than methane, such asethane, propane, butanes, pentanes, C₆ ⁺, etc, as well as usually aproportion of methane. At least part of the heavier stream is commonlyused to produce a natural gas liquid product or products, such asusually C₃, C₄, etc.

The distillation column is preferably a natural gas liquid recoverycolumn, generally for C₃ and C₄ hydrocarbons, optionally C₅ ⁺hydrocarbons, and which generally operates at a low pressure.

Following its separation in the distillation column, at least a part ofthe gaseous stream, usually all of the gaseous stream, is compressed.Said compression may be considered a ‘recompression’ where the feed gasis provided in a pressurized form. It is desirable to compress orrecompress the gaseous stream as it is easier to liquefy natural gas athigh pressure.

The compression of the gaseous stream can be carried out by one or morefeed compressors such as natural gas booster compressors. In oneembodiment of the present invention there are two feed compressors.

In another embodiment to the present invention, one, usually the first,feed compressor is mechanically interconnected to an expander adapted toexpand the feed gas prior to its passage through the distillationcolumn, so as to be partly, substantially or wholly driven thereby. Thisprovides a more efficient arrangement.

Drivers for a compressor are known in the art. They may be a singlegenerator, or a combination of generators. They include gas turbines,steam turbines and electric motors, and the generator or combination canbe adapted to suit the apparatus, arrangement or system, some of whichmay include generator assistance from one or more other parts of theapparatus. In one arrangement, there is an auxiliary engine such as anelectric motor to help start-up, and a gas turbine for the main runningfor the driver.

In one embodiment of the present invention, the cooling of thecompressed stream involves liquefying the compressed stream therebyobtaining a liquefied hydrocarbon stream such as liquefied natural gas.

The present invention also provides a method of treating a hydrocarbonstream such as natural gas from a feed stream comprising at least thesteps of:

-   (a) liquefying the feed stream by cooling the feed stream against    one or more refrigerants being in one or more refrigerants circuits    involving one or more refrigerant compressors, to provide a    liquefied feed stream;-   (b) passing the liquefied feed stream through an end separation    vessel to provide an end gaseous stream and an end liquid stream;    and-   (c) compressing at least a part of the end gaseous stream through    one or more end compressors to provide a compressed end gaseous    stream;    wherein at least one of the refrigerant compressors in step (b) at    least one of the end compressors in step (c) are mechanically    interconnected and are arranged to be driven by a common driver.

This method has similar advantages as hereinbefore described, inparticular higher process efficiency and lower capital and runningcosts.

The present invention includes a combination of any and all of themethods hereinbefore described, and mechanical interconnection of morethan two compressors with a common driver.

The present invention also provides apparatus for treating a hydrocarbonfeed stream such as natural gas, the apparatus at least comprising:

a distillation column having an inlet for the feed stream and a firstoutlet for a gaseous stream and a second outlet for a C₂ ⁺ liquidstream;

one or more feed compressors for compressing at least a part of thegaseous stream; and

a common driver for driving one or more of the feed compressors with oneor more separate refrigerant compressors for one or more separaterefrigerant circuits.

Preferably, the apparatus includes a cooling system which may involve atleast one pre-cooling stage and at least one main cooling stage, eachstage including at least one refrigerant circuit and at least onecompressor.

Also preferably, the cooling system involves or comprises a liquefyingsystem, more preferably able to provide an LNG stream.

Optionally, at least one compressor of both the pre-cooling and maincooling refrigerant circuits are also mechanically interconnected andare arranged to be driven by a common driver.

Embodiments of the present invention will now be described by way ofexample only, and with reference to the accompanying non-limitingdrawings, in which:

FIG. 1 is a general scheme of a treatment process according to oneembodiment of the present invention;

FIG. 2 is a general scheme of a treatment process according to a secondembodiment of the present invention; and

FIG. 3 is a general scheme of a treatment process according to a thirdembodiment of the present invention.

For the purpose of this description, a single reference number will beassigned to a line as well as a stream carried in that line. The samereference numbers refer to similar components.

Referring to the drawings, FIG. 1 shows a treatment process for ahydrocarbon feed stream, such as a pre-treated natural gas streamwherein one or more substances or compounds, such as sulfur, sulfurcompounds, carbon dioxide, and moisture or water, are reduced,preferably wholly or substantially removed, as is known in the art.

Following any pre-treatment, the feed stream 10 could be expandedthrough a vapour expander 22 and then fed via inlet 52 into adistillation column 12 being a natural gas liquid recovery column, whichpreferably operates between 0° C. and −100° C., and at an above ambientpressure such as 10-30 bar.

The expander 22 can be in the form of a turbine. It reduces the pressureof the feed gas 10.

In the distillation column 12, the expanded feed stream 10 a isseparated into a gaseous stream 20, generally being a methane enrichedstream and provided through a first outlet 54, and a C₂ ⁺ liquid stream30, generally being a heavier hydrocarbon rich stream and providedthrough a second outlet 56.

The gaseous stream 20 from the first outlet 54 can then be re-compressedto make its subsequent cooling, preferably liquefaction, easier.Preferably, prior to re-compression, the gaseous stream 20 isheat-exchanged (not shown) against feed stream 10 to cool feed stream10. The recompression may be to the same or similar pressure of the feedstream 10 before it entered the expander 22, or may be different. InFIG. 1, the recompression can be achieved in two stages. Firstly, thegaseous stream 20 is passed through a first feed compressor 14. Thisfirst compressor 14 is driven by the expander 22 via an interconnectingdrive shaft 24, so recovering at least some of the energy created by theexpansion of the feed gas 10 passing through the expander 22.

Thereafter, the part-compressed gaseous stream 20 a is passed through asecond feed compressor 16. Such second compressor 16 is usually largerthan the first feed compressor 14.

Hitherto, the second feed compressor 16 has been driven by its owndedicated driver, generally being a gas or steam turbine, and usuallywith an electric start-up motor as well. As mentioned above, everyseparate driver increases the capital and running costs of the plant.Indeed, thirty to forty percent of the capital cost in a liquefiednatural gas (LNG) plant lies in the cooling plant proper. Thusminimizing the capital cost of a cooling operation is particularlyadvantageous.

An advantage of the present invention is to mechanically interconnectthe second feed compressor 16 with a refrigerant compressor 18 of one ofthe refrigerant circuits described hereinafter. Preferably, the twointerconnected compressors 16, 18 are driven by a common driver 28. Thedriver 28 could be a gas turbine having an associated starter/helpermotor.

According to an embodiment of the present invention involving two ormore feed compressors, at least one of the feed compressors ismechanically interconnected with at least one of the refrigerantcompressors. Where there are multiple feed compressors and the first ismechanically interconnected with an expander adapted to expand the feedstream prior to separation, then it is the largest feed compressor whichis preferably driven with the refrigerant compressor.

Following recompression of the gaseous stream 20 through the first andsecond compressors 14, 16, the compressed stream 40 is optionally firstcooled by one or more ambient water and/or air coolers (not shown) knownin the art, followed by cooling against one or more refrigerants asdiscussed further below.

The cooling of the compressed stream 40 can be carried out by a coolingsystem having or including any number of cooling stages. One commonarrangement involves a pre-cooling or first cooling stage, and one ormore, usually one, main cooling stages. Each cooling stage generallyinvolves at least one refrigerant, which refrigerant(s) are generallybeing circulated in a refrigerant circuit(s). Each cooling stage mayalso involve one or more steps, levels or sections, and there may alsobe a final sub-cooling stage.

In the embodiment shown in FIG. 1, the cooling is or involves liquefyingof the compressed stream 40 by a liquefying system which has one or morecooling and/or liquefying stages. This could involve a pre-cooling stage26 and a main cooling stage 62. The pre-cooling stage 26 involves apre-cooling refrigerant circuit 32 which has at least one separaterefrigerant compressor 18 for compressing its refrigerant, such aspropane or a mixed refrigerant, to a higher pressure. A heat exchanger,which could be one or more air coolers or other condensers, is provideddownstream of the compressor 18 to cool the refrigerant with heatexchanged with a coolant, typically air and/or water.

Whilst a single refrigerant compressor 18 is shown in the pre-coolingrefrigerant circuit 32 in FIG. 1, it is envisaged that two or moreseparate or single casing compressors, which could optionally also bemechanically interconnected, may be used, optionally arranged on acommon drive shaft.

The refrigerant compressor 18 of the pre-cooling refrigerant circuit 32is driven by a gas turbine 28 which could have an associatedstarter/helper motor. The second (and main) feed compressor 16 ismechanically interconnected to the separate refrigerant compressor 18 ofthe pre-cooling refrigerant circuit 32, preferably by being provided ona common drive shaft, whereby the gas turbine 28 also drives the secondfeed compressor 16, thus avoiding the need for two separate gas turbinesor other drivers and associated capital and running costs.

The distribution of power from the gas turbine 28 between thepre-cooling refrigerant compressor 18 and the second feed compressor 16can be freely chosen, such that the optimal power balance can beachieved. In particular, it is desired for the compressor power inputfrom the gas turbine 28 to be as close as possible to the optimal ratiofor natural gas liquefaction. Large industrial gas turbines are knownwhich are able to provide such power, and a changeable power inputallows for variation in loads of the compressors where non-steady stateconditions are involved.

Typically, the liquefying system also includes a main cooling stage 62which has a separate refrigeration circuit 64, and which generally alsoincludes one or more separate refrigerant compressors 66. A non-limitingexample of a typical main refrigerant is a mixture of compounds havingdifferent boiling points in order to obtain a well-distributed heattransfer. One mixture is nitrogen, ethane and propane. Like therefrigerant of the pre-cooling circuit 32, the main refrigerant isseparate from the feed stream 10, compressed stream 40 and itsdownstream pre-cooled form 50.

The main cooling stage 62 could have two or more compressors forcompressing the main refrigerant. The main refrigerant could then bepassed through a heat exchanger where it is cooled by heat exchange witha coolant, such as water. The main refrigerant could then be furthercooled by heat exchange with the refrigerant of the pre-coolingrefrigerant circuit 32. In the or a heat exchanger of the main coolingstage 62, the expansion of the main refrigerant further cools andoptionally liquefies the pre-cooled stream 50 from the pre-coolingprocess by heat exchange, to provide a further cooled, preferablyliquefied, product stream 60.

It is possible that one or more of the main refrigerant compressors 66could be mechanically interconnected with the pre-cooling refrigerantcompressor 18 of the pre-cooling refrigerant circuit 32, and/or thesecond feed compressor 16, so as to be driven by a common driver,possibly on a common drive shaft.

FIG. 2 shows a second arrangement for treatment of a hydrocarbon streamprior to any cooling and/or liquefaction. Compared to the arrangementshown in FIG. 1, the feed stream 10 is cooled prior to its expansionthrough the expander 22. The cooling can be carried out by an upstreamor prior cooling stage 34 wherein the feed stream 10 is cooled againstan upstream refrigerant circuit 36. The upstream refrigerant circuit 36involves a compressor 38 for compressing its separate refrigerant mediato a higher pressure.

Similar to FIG. 1, in the arrangement in FIG. 2, the expanded feed gas10 a is fed via an inlet 52 into a distillation column 12, therebyproviding a gaseous stream 20 via a first outlet 54, and providing a C₂⁺ liquid stream 30 via a second outlet 56. The gaseous stream 20 canthen be recompressed through a first feed compressor 14 and second feedcompressor 16. The compressed light stream 40 can then be cooled and/orliquefied as is known in the art, such as the liquefying system of FIG.1.

In the arrangement shown in FIG. 2, the second feed compressor 16 ismechanically interconnected with the compressor 38 in the upstreamrefrigerant circuit 36 for the upstream cooling stage 34. Preferably,the two interconnected compressors 16, 38 are driven by a common driver42. The driver 42 could be a gas turbine having an associatedstarter/helper motor.

The arrangement shown in FIG. 2 has an advantage like that shown in FIG.1, that is avoiding the need for two separate gas turbines or otherdrivers for the second feed compressor 16 and an upstream refrigerantcompressor 38. As with the arrangement shown in FIG. 1, the distributionof power from the gas turbine 42 between the compressors 16, 38 can befreely chosen, such that the optimal power balance can be achieved.

Liquefied natural gas 60 from a liquefying system can be passed into afinal separator wherein vapour can be removed for use as fuel in theplant, for example for the gas turbines running the various compressors,and a liquefied natural gas product can be transferred to a storagevessel or other storage or transportation apparatus.

FIGS. 1 and 2 exemplify two possible arrangements of the presentinvention for commonly driving at least one of the feed compressors withone or more separate refrigerant compressors for one or more separaterefrigerant circuits.

FIG. 3 shows a third scheme for treating a hydrocarbon feed gas stream100, particularly the end flash processing of an LNG stream. One sourceof the hydrocarbon feed gas stream 100 is the compressed stream 40 shownin FIGS. 1 and 2.

Liquefaction of a hydrocarbon stream 100 by a liquefying system is knownby the skilled person in the art. Liquefaction can be carried out in anumber of stages, and for the sake of simplicity only, FIG. 3 shows afinal sub-cooling stage 102 only. The sub-cooled stream 110 can passthrough an expander 104 to provide stream 110 a, and a water and/or aircooler 106 to provide stream 110 b, which passes via inlet 122 into anend separation vessel 108, in this instance being an end flash vesselknown in the art.

In general, an end flash system such as that shown in FIG. 3 can be usedat the downstream end of the sub-cooling stage 102 to optimize liquefiednatural gas (LNG) production. It usually includes an end compressordriven by a separate electric drive motor. The power needed to drive theend compressor is a usually smaller than the required compressor powerfor the sub-cooling stage.

The end separation vessel 108 has a first outlet 124 to provide a liquidstream 120 such as LNG, which, via a pump 128, can create a final LNGstream 130 for storage and/or transportation.

From a second outlet 126 of the end separation vessel 108 there isprovided an end gaseous stream 140, which could be combined with, forexample, a boil-off gas stream 150 known in the art. The combined stream160 can be compressed by an end compressor 114 to provide a useablestream 170, such as for fuel gas.

The sub-cooling stage 102, involves a refrigerant circuit 132 having afirst refrigerant compressor 116. Optionally, the sub-coolingrefrigerant circuit 132 also includes an air or water cooler 117.

In the arrangement shown in FIG. 3, the first refrigerant compressor 116is mechanically interconnected with the end compressor 114. Preferably,the two interconnected compressors 114, 116 are driven by a commondriver 134. The driver 134 could be a gas turbine having an associatedstarter/helper motor.

The arrangement shown in FIG. 3 has an advantage like that shown inFIGS. 1 and 2, that is avoiding the need for two separate gas turbinesor other drivers for the end compressor 114 and first refrigerantcompressor 116. As with the arrangement shown in FIGS. 1 and 2, thedistribution of power from the driver 134 between the compressors 114,116 can be freely chosen, such that the optimal power balance can beachieved.

The liquefaction in FIG. 3 may involve other cooling stages such aspre-cooling and main cooling stages. Any or each such cooling stage ofthe liquefaction may involve one or more refrigerant circuits, andinvolve one or more refrigerant compressors. It is possible that one ormore of the other refrigerant circuit compressors used in theliquefaction, from any stage thereof, could be mechanicallyinterconnected with the end compressor 114, so as to be driven by acommon driver, possibly on a common drive shaft.

The following Table provides example temperature, pressure, flowrate andphase data for an embodiment of the present invention exemplified inFIG. 1.

Temperature Pressure Flowrate Phase Stream ° C. Bar kmol/s — 10 −28 5717 vapor   10a −69 22 17 mixed 30 −58 22 3 liquid 20 −76 22 18 vapor  20a 48 29 18 vapor 40 88 73 18 vapor 50 −27 71 18 vapor 60 −150 66 18liquid

The person skilled in the art will understand that the present inventioncan be carried out in many various ways without departing from the scopeof the appended claims.

1. A method of treating a hydrocarbon stream from a feed streamcomprising at least the steps of: (a) passing the feed stream through adistillation column to provide a gaseous stream and a C2+ liquid stream;(b) compressing at least part of the gaseous stream through one or morefeed compressors to provide a compressed stream; and (c) commonlydriving at least one of the feed compressors with one or more separaterefrigerant compressors for one or more separate refrigerant circuits,by mechanically interconnecting said compressors.
 2. A method as claimedin claim 1 wherein the distillation column is a natural gas liquidrecovery column.
 3. A method as claimed in claim 1 wherein the feedstream is expanded prior to passing through the distillation column. 4.A method as claimed in claim 1 wherein the compressing of step (b)involves first and second feed compressors.
 5. A method as claimed inclaim 1 further comprising the step of: cooling the compressed stream bypassing the compressed stream against one or more refrigerants being inone or more of the refrigerant circuits.
 6. A method as claimed in claim5 wherein the second feed compressor is mechanically interconnected witha refrigerant compressor of one or more of the refrigerant circuitscooling the compressed stream.
 7. A method as claimed in claim 5,wherein the cooling of the compressed stream involves at least twocooling stages, each stage including at least one refrigerant circuit.8. A method as claimed in claim 7 wherein the cooling of the compressedstream involves one pre-cooling stage and one main cooling stage, andthe or a feed compressor of step (b) is mechanically interconnected witha refrigerant compressor of the pre-cooling refrigerant circuit.
 9. Amethod as claimed in claim 5 wherein the cooling of the compressedstream involves liquefying the compressed stream thereby obtaining aliquefied hydrocarbon stream.
 10. A method as claimed in claim 1 furthercomprising the step of: cooling the feed stream upstream of step (a) bypassing the feed stream against one or more refrigerants being in one ormore of the refrigerant circuits.
 11. A method as claimed in claim 10wherein the or a feed compressor of step (b) is mechanicallyinterconnected with a refrigerant compressor of the refrigerant circuitcooling the feed stream.
 12. A method as claimed in claim 1 furthercomprising the step of: cooling the feed stream upstream of step (a)against at least part of the gaseous stream.
 13. Apparatus for treatinga hydrocarbon stream from a feed stream, the apparatus at leastcomprising: a distillation column having an inlet for the feed streamand a first outlet for a gaseous stream and a second outlet for a C2+liquid stream; one or more feed compressors for compressing at least apart of the gaseous stream; and a common driver for driving one or moreof the feed compressors with one or more separate refrigerantcompressors for one or more separate refrigerant circuits.
 14. Apparatusas claimed in claim 13, wherein the commonly driven compressors aremechanically interconnected and arranged on a common drive shaft of thedriver.
 15. Apparatus as claimed in claim 13, wherein the apparatusincludes an expander to expand the feed stream upstream of thedistillation column.
 16. Apparatus as claimed in claim 15 wherein theexpander is mechanically interconnected to one or more of the feedcompressors and is partly, substantially or wholly driven thereby. 17.Apparatus as claimed in claim 13, wherein the apparatus further includesa cooling system for cooling the gaseous stream, which cooling systeminvolves at least one pre-cooling stage and at least one main coolingstage, each stage including at least one refrigerant circuit and atleast one refrigerant compressor.
 18. Apparatus as claimed in claim 15,wherein one feed compressor of step (b) is mechanically interconnectedwith a refrigerant compressor of a pre-cooling refrigerant circuit. 19.Apparatus as claimed in claim 15, wherein at least one refrigerantcompressor of both the pre-cooling and main cooling refrigerant circuitsare mechanically interconnected and are arranged to be driven by saidcommon driver.
 20. Apparatus as claimed in claim 13, wherein the coolingsystem includes a liquefying system to obtain a liquefied hydrocarbonstream.